Electrical heating resistance and method of making same.



40: v E'relaxationdeprives the frail resistance ma UNITED STATES PATE T OFFICE.-

i ILLIAM s. HADAWAY, JEQ, OF EAST ORANGE, NEW JERSEY.

.i .i ITRiCAL HEATIN G RESISTANCE AND METHODOF MAKING SAME.

SPEoIFIcA'rION forming part of Letters Patent No. 670,671, dated March as, 1901.

' Original application filed September 24, 1898, Serial lio. 691,770. Divided and this application filed-December 1,1900. Serial 1 w. I No. 39,024. (No specimens.)

' 5 of New Jersey, have invented a certain new I and useful Improyenient in Electrical Heating Resistance and Method of Making the Same, of which the following is a specification, this being adivision of my pending applica- .-j;ot,tion, Serial No. 691,770, filed September 24,

iA'greatvariety of compositions of matter has been hitherto, put into use in making electrothermal resistances for heaters.

timately mixed with some'non-conducting powder which serves to, reduce the conductivity of the mass inproportion as moreor so less thereof is employed.

In-man y kinds of tools'a very high tempera tn re is'required, and hitherto electric heating ,by ineansq-of eleetrothe'rmal-resistance conductors'h'as not been possible in such connec- 5 tions, o'wing, mainly, to two related causes-. I first, because the ohmic resistance of the com- ;poundsghitherto employed has been found to decrease rapidly asthe temperature was raised, and, second,'because the com positions. 3o'hsed rapidly-deteriorated and finally fell to ,pieces and became useless when so heated.

The princi pal causes to which these difiiculties are ascribable are the fact that the various powders used to dilute the carbon have always 35" formed carbids with the same when subjected to very high temperatures, the reduction in volume which occurs when the compounds hitherto used are frequently subjected to very high temperatures, and the relaxation of pressure in part due to this contraction, which .terial of necessary support.

My invention embodies the discovery of a material which mixed with powdered graphite or'other forms-of carbon will not form anarbid when heated and which is already in its state of maximum density, thus preventing further-contraction .in use.

My improved compound is composed of an 5o intimatelimixture of finely-powdered carbon,

preferably graphite, and finely powdered of the appropriatebinding cement-s.

In .15 general these consist of finely-powdered carbon, serving as the conducting element, in-

.crystalline magnesium oxid united by any.

ances of any desired shape and size can be molded from this composition, as is well understood in the art.

Resist- 'In order to produce a thoroughly-durable compound which can be relied upon to preserve a predetermined specific ohmic resistance unchanged ,at very high temperatures,

,I prefer to employ thefollowing steps in pre- As most.

an electric fuifnace and fused by the are, so a as to form a crystalline mass of maximum density on cooling. These crystals should beseparatedfrom the amorphous magnesia surrounding them as they come from the fu r,- nace and are reduced to a very fine powder. The graphite is very finely powdered and then-thoroughly baked at a temperature exceeding that to which it is designed to be sub- I prefer, indeed, to bake jected in practice. the graphite at the same temperature as that to which the magnesia is subjected in fusion, taking the usual precautions to exclude the air. By thus baking the constituents of my resistance compound at a"temperatur e' far above that employed in its practical use Ired'uce them to their ma 'imum density, and thus avoid injurious contraction during use. The two powders are thoroughly mixed in anywell-known fway inv such proportions as areappropriate to the voltage of the heatingcurrent, size and shape of resistances, degree of heatdesired, and other conditions. I have found the mixture of ten per cent. of graphite and ninety percent. of magnesia suitable for use with a one-hundred-and ten-volt current in flat iron work where a temperatur of about 900 Fahrenheit is required. The mixture so produced is molded into the required shape with molasses-water or other approriate cementing material, as well understood l the art,- a'nd is then after baking ready for e! What I claim is-;

1. An electrotherma-l-resistance compound msisting of a mixture of powdered carbon 1d powdered crystallized magnesia.

2. The process of forming an electric-restance compound for electric heaters which nsists in mixing powdered carbon and poware'd crystallized magnesia and baking the ixture at at nperature higher than that innded to be p 'odnced by the resistance comu'nd in practice. I

3. The process of Ananufactlh'ing a resist- 00 com pound which consists infusing magsia, separating the crystallized portions of intended in precti ce, and mixing the two powders.

4. The process of mannfacturing a resist;

ance compound which consists in fusing magnesia, separating the crystallized portions of the resulting mass' 'afterfcooling, reducingthe same to powder, mixing said powder withfinelyrpowdered carbon and uniting the mix-' ture by neansvof, an appropriate cement. WILLIAM s. HADAWAY, J'R;

Witnesses: I

P. '1. TUNISON, H.-S. MACKAYE. 

